Field of the Invention
This disclosure relates to a roller member used for an image forming apparatus, a roller supporting mechanism provided with the roller member, and a metallic shaft used in the roller member. An image forming apparatus is an apparatus that forms images on recording media.
Examples of an image forming apparatus include, for example, electrophotographic copying machines using an electrophotographic image forming process, electrophotographic printers (LED printers, laser beam printers), facsimile apparatuses, and word processors.
Description of the Related Art
In the related art, an electrophotographic image forming apparatus (hereinafter, referred to as an image forming apparatus) includes a photosensitive member and a process device configured to act on the photosensitive member. Examples of the process device include a voltage application apparatus configured to apply electric charge on the photosensitive drum, a developing device configured to supply developer (hereinafter, referred to as “toner”) to the photosensitive drum, and a cleaning device configured to clean toner failed to be transferred and remaining on a surface of the photosensitive drum.
Examples of a charging device in the voltage application apparatus include a roller charging system using a roller member. In the roller charging system, charging of the surface of the photosensitive drum is achieved by bringing a charging roller, which is a conductive resilient roller, into bias abutment with the photosensitive drum and applying a voltage thereto. The charging roller generally has a form having a resilient layer covering a metallic shaft over the entire area in a longitudinal direction other than both ends (Japanese Patent Laid-Open No. 2013-109209, pp. 11, FIG. 2).
Examples of the metallic shaft of the charging roller include a form using a cylindrical-shaped metallic shaft (Japanese Patent Laid-Open No. 2010-230748).
However, in the case of manufacturing the cylindrical-shaped metallic shaft by bending a metallic plate by a press work or the like, a mating portion (an opposed portion where one end portion and the other end portion of the metallic plate oppose each other) extending along an axial direction is present on the metallic shaft. In order to increase the strength of the metallic shaft at this time, a configuration in which a projection and depression area is provided on the mating portion and one end portion and the other end portion of the metallic plate are engaged by the projections and depressions of the metallic plate is conceivable. However, in this projection and depression area, if the metallic shaft is rotatably supported by the bearing portion, the bearing portion is caught by the projection and depression area, and hence a rotational sliding resistance may increase.
Therefore, reducing the resistance at the metallic shaft and the bearing portion at the time of rotation of the roller member while increasing the strength of the metallic shaft is required.